This invention relates to an adjustable hospital bed having a transmission for coupling a single common motor drive to selected ones of a plurality of adjusting mechanisms to effect operation thereof to achieve different bed adjustments. More particularly, the invention relates to an arrangement for decoupling the motor drive from those of the adjusting mechanisms that should not be operated.
Adjustable hospital beds are usually vertically movable, by means of adjusting or lift mechanisms, so that the mattress supporting structure may be established at a selected desired height, within a range of permissible heights, from the floor. The lowermost level is most convenient when a patient is entering or leaving the bed. On the other hand, the uppermost height is generally preferred for examination and treatment of the patient. To enhance the patient's comfort, the mattress support is divided into a series of individually adjustable sections or panels that may be positioned, by independently operable adjusting or lift mechanisms, to provide a desired contour or configuration. For example, one adjusting mechanism may tilt a back section so that the patient's back and head may be raised, while another lift or adjusting mechanism may adjust a knee section of the mattress support to raise the patient's knees. In addition in many adjustable hospital beds the entire mattress supporting structure may be tilted or canted to either the trendelenburg position (head end down, foot end up) or to the reverse trendelenburg position (head end up, foot end down). The bed is adjusted to the trendelenburg position when the patient goes into shock, whereas the reverse trendelenburg position is employed for drainage. The various adjusting mechanisms are operator-controlled, meaning that they can be controlled by a doctor, nurse, attendant and/or patient.
When a hospital bed has a variety of different characteristics or bed functions that may be adjusted by a single common drive, usually a reversible or bidirectional electric motor, a transmission has been employed to couple the common motor drive to a selected one of a series of adjusting mechanisms, each of which controls a different bed adjustment or characteristic. This may be facilitated by a series of clutches each of which, when engaged, couples the motor drive to an associated adjusting mechanism. Power may thus be transmitted through an engaged clutch to the selected adjusting mechanism to effect actuation thereof which in turn adjusts the associated bed function. When two or more different bed adjustments are desired by the operator (for example, when it is desired to raise the patient's back and knees), the clutches for the back and knee adjusting mechanisms may be engaged one at a time in order to make the necessary adjustments.
The clutches respectively assigned to the several adjusting mechanisms must be reliable in operation, engaging when actuated and disengaging or releasing when the actuation is removed. Generally, each clutch is spring biased, being held disengaged by means of an appropriate spring. To engage a clutch, a solenoid is energized to overcome the force of the spring and to move the mating surfaces of the clutch into engagement, thereby coupling the motor drive to the adjusting mechanism with which the clutch is associated. When the adjusting mechanism has completed the desired bed adjustment, the solenoid is de-energized so that the clutch restoring spring will separate the mating surfaces, thereby disengaging the clutch. Of course, it is imperative that the clutch never latches or locks into an engaged condition such that it remains in that condition even after the solenoid is de-energized. The clutch must release or disengage when the solenoid de-energizes. Otherwise, the next time the operator initiates a new and different bed adjustment, the wrong adjusting mechanism will operate and an undesired bed adjustment will be made. In other words, since the previously used adjusting mechanism is interlocked to the drive motor, via a latched clutch that failed to release, that undesired adjusting mechanism will be actuated to produce an erroneous and unwanted bed adjustment.
Such faulty clutch operation has been overcome in the past by employing a relatively heavy spring which exerts a high restoring force on the movable clutch member so that it will return to its disenaged condition as soon as the controlling solenoid is de-energized. Unfortunately, a large, high-powered solenoid is required to counter the strong force of the restoring spring. Hence, reliable clutch operation has been obtained in the past at the expense of high cost, high power switching, low efficiency and high noise.
In sharp contrast, the unique hospital bed of the present invention includes a transmission which couples a common motor drive only to the selected adjusting mechanisms that should be operated, the drive being decoupled from those adjusting mechanisms that should not be operated. Moreover, and of major importance, the coupling arrangement is extremely reliable and efficient in operation, and is low in cost, power consumption and noise.